Lubrication improvements via diffusion

ABSTRACT

The extreme pressure properties of ferrous metals can be increased by coating the metal with iron sulfide or chloride or mixtures thereof then heat treating the coated metal at a temperature in the range of 900*-2,000* F. for 1/2 to 24 hours. When metal Falex pins and jaws are treated in the above fashion they have longer running times, i.e., up to 11 times, than untreated pins and jaws under the same conditions in a standard Falex testing apparatus.

United States Patent Inventor Edward M. Kohn llaveriord Township, Delaware County, Pa.

Appl. No, 757,783

Filed Sept. 5, 1968 Patented Dec. 21, 1971 Assignee Sun Oil Company Philadelphia, Pa.

LUBRICATION IMPROVEMENTS VlA DIFFUSION 8 Claims, No Drawings US. Cl Mil/6.14, 148/624 Int. Cl C23f 7/24 Field of Search 148/6. 1 4, 6.24

References Cited UNITED STATES PATENTS 2,266,379 12/1941 Floyd l48/6.24 X 2,707,159 4/l955 Foucry et al l48/6.24 X

Primary Examiner Ralph S. Kendall Attorneys-George L. Church, Wilmer E. McCorquodale, Jr.,

Donald R. Johnson and Kenneth H. Johnson LUBRICATION IMPROVEMENTS VIA DIFFUSION The present invention is a process for treating ferrous metals to improve the lubricant characteristics of the treated ferrous metals. More particularly, the ferrous metals are treated with sulfur, chlorine or mixtures thereof.

It has long been an aim of metalurgists to improve the performance of fabricated ferrous pans in regard to lubrication. This has been a pressing problem, for example, in the breakin" period for internal combustion engines and gear systems. During this period, extreme pressure additives in the lubricants can be detrimentally corrosive. One solution has been to coat these parts with a thin layer of sulfur which reacts with the ferrous metal to give a layer of black ferrous sulfide or to coat on a nonferrous sulfide. Such coatings have been applied in a number of ways, for example:

U.S. Pat. No. 1,562,138 to Becker issued Nov, 17, 1925, shows the deposition of ferrous sulfide onto steel wool by heating the steel wool in an oil bath containing sulfur at a temperature of 300 to 500 F.

Snow in U.S. Pat. No. 2,263,905 issued Nov. 25, 1941, used a flash coating method wherein an aqueous solution containing active sulfur is sprayed onto the hot metal surface.

Floyd in U.S. Pat. No. 2,266,379 issued Dec. 16, 1941, applied a coating of sulfur to metal parts by heating the part in an oil bath containing active sulfur at 200 to 300 F. and found that test pins bore substantially increased loads before failure.

Neely, Farrington and Borsoff found in U.S. Pat. No. 2,297,909 issued Oct. 6, 1942, that the performance of ferrous gears in the break-in" period was improved even in noncorrosive lubricants, i.e., no EP additives, by treating the ferrous metal with sulfur to form iron sulfide films. The films can be applied by treatment with gases or liquids containing sulfur or which yield sulfur at the temperatures of operation, which are around 300 to 500 F.

Recently Takahashi in U.S. Pat. No. 3,144,359 issued Aug. 1 l, 1964, sulfurized the surface of ferrous metals by immersing the metal in molten sulfur at temperatures of 120 to 445 C.

All of these prior art attempts to improve the extreme pressure properties of ferrous metals have been limited to the formation of a surface layer of iron sulfides. One problem that constantly plagues this approach is the susceptibility of this fragile coating to removal from the metal part. Thus, a great deal of effort has been directed to developing techniques by which the sulfurized layer is firmly adhered to the metal.

The process of the present invention achieves the benefits of sulfurized metal parts, but without the necessity or concern for protecting the iron sulfide coating during use. Briefly stated, the present invention is a process for treating ferrous metal comprising the steps of a. forming a coating comprising iron sulfide, iron chloride or mixtures thereof on said ferrous metal and.

b. subjecting said coated ferrous metal to a temperature in the range of 900 to 2,000" F.

Stated differently the present invention takes the ferrous metals having sulfurized and/or chlorinated surfaces and heats these previously treated metals at extremely high temperatures. After the high-temperature treatment, the coating can be removed, although it need not be. The result is that ferrous metals treated according to the invention exhibits better load properties than similar ferrous metal parts not having sulfurized and/or chlorinated treatment.

The theory proposed to account for this result, but of course not to limit the claims, is that there is a diffusion of sulfur and/or chlorine into the ferrous metal. Thus, there is no need to depend on the fragile surface coating for improved lubricity.

The phenomenon of sulfur diffusing into iron has been observed previously. Recently Ainslie et al., ACTA Metallurgica, Vol. 8, pp. 523-527 and 528-538 (1960) carried out such diffusions at high temperatures to determine their nature. 1n their work, Ainslie et al., employed FeS and hydrogen with very pure iron at 890 C. The hydrogen reacted with FeS to form H,S which sulfurized the iron. Formation of FeS on the test iron was avoided.

In the present process the iron sulfide or chloride can be fonned on the ferrous metal by any of the prior art processes, for example, those in the previously mentioned U.S. patents. A method that is preferred because of its ease and simplicity is that wherein the ferrous metal is immersed in a mineral oil containing active sulfur and/or active chlorine.

The sulfur can be naturally occurring or added to the oil. A suitable oil would have between 0.5 and 15 percent sulfur. The iron sulfide is formed by heating the oil at a temperature in the range of l00-500 F. This heating is usually carried on for about 2 to 48 hours or until there is visible coating of sulfide on the metal.

The chloride coating can also be obtained in several ways, for example, contacting the hot metal (l00500 F.) with gaseous chloride or HCl or in a heated bath. However, it has been found advantageous to use chlorinated hydrocarbons particularly paraffins which can be dissolved in oil into which the metal is immersed for heating and coating. This method is particularly advantageous when a mixed coating of sulfides and chlorides is desired. The conditions of temperature and time are essentially the same for chloride coatings as for sulfide coatings. Suitable oil would contain 0.5 to 15 wt. percent active chlorine.

As stated the metal is any ferrous metal or alloy in any of its varied forms such as cast, forged, heat treated, mechanically worked, etc.

The sulfide and/or chloride coated metals are then subjected to a high-temperature heat treatment. The temperature of this treatment is about 900 to 2,000 F.

The diffusion of the sulfur and chlorine into the ferrous metal has been found to proceed at both atmospheric and superatmosphere pressures. No observed effect has been found to be dependent on pressure. The atmosphere for the diffusions can be for example argon, neon or air. Thus, so far as observed it is the high-temperature treatment per so that is responsible for the diffusion. The high-temperature treatment is usually carried on from A to 24 hours or more. The temperature appears to have more effect on the effectiveness of the treatment than the duration as can be seen from table 11.

Prior to the high-temperature treatment the coated metal can be cleaned, particularly where an oil bath was used in the coating step. Naphtha or a similar solvent can be used to remove any adhering oil or grease. Metal parts treated in accordance with the instant invention will provide improved load carrying properties in oil containing no extreme pressure additives and will contribute additional EP improvement to those oils containing such additives. Care should be taken in handling the coated metals since the coating is relatively fragile.

The following examples illustrate the invention and its improvement.

EXAMPLE 1 The base oil employed in the runs was the same and had the following properties:

nil

The sulfurizing oil is the base oil to which 0.9 wt. percent active of sulfur has been added.

In order to provide a means for testing the improved results the ferrous metal employed was Falex V Blocks and Falex Pins having the following properties:

Fnlex V Blocks Batch B Composition MS] I37 steel Rockwell Hardness R ZO Surface Finish 3-6 RMS Block angle 96 Falex Number 8 Test Pins Batch Composition SAE 3135 steel Rockwell Hardness R, 87-90 Surface Finish I0 RMS. max.

Surface Coating Pins and jaws were cleaned well in boiling naphtha and then surface coated with sulfur. This was done by heating them in the sulfurizing oil at 360 F. for 16 hours then again in fresh sulfurizing oil for an additional 16 hours. Controls were prepared by heating the pins and jaws in the base oil for the same length of time and at the same temperature as the sulfurized pins and jaws. The sulfided pins and jaws were coated with a black coating. The control had a brown-gold stain. The coated pins and jaws were carefully cleaned with naphtha. High-Temperature Treatment Groups of three pins and six jaws were sealed in an ASTM A-3 12 A181 Type 347 stainless steel pipe having dimensions of treatments were carried out at 1,000 1,200 l,200 and 1.400 F 1% hours, 6% hours and 24 hours as follows:

TABLEI Temperature F. Treatment hours V; 6 ii 24 l .000 X I ,200 X X X l .400 X X treatment The Falex tester basically consists of a drive shaft into which the one-half inch or journal pins is placed and secured with a brass shear pin. The free end of the pins is in contact with a set of jaws at 180 to each other. The test pin is rotated against the two stationary V blocks to give a four-point contact. The pressure applied by the jaws is adjustable and controllable. The

jaws and the pin are immersed in the lubricant cup which in about l2 l%-inch pipe by welding on end plates. One end the present tests contained the base oil. The test pin was plate had two tubes serving as inlet and outlet for argon gas. The sulfurized and nonsulfurized control pins and jaws were not mixed during this treatment. The gas was dry, high-purity 99.996 argon. A steel wool plug on the inlet tube scavenged driven at 290 rpm. The pin rotated freely at first. The load was applied to the V blocks through a nutcracker action lever arm and spring gauge. The load was slowly run up to 750 pounds gauge and maintained at that pressure. The load was out any oxygen or moisture that might be present in the argon. checked every minute and returned to 750 pounds if it fell The steel wool had been previously washed in acetone.

The heat cycle consisted of a slow temperature rise up from room temperature to the treat temperature, usually taking about 1 hour. After holding at the desired temperature for the below that value. Running time to failure was observed and is shown in table [1. In this set of runs, failure in each instance of the treated pins was mechanical failure of the Falex pin which sheared in the vicinity of the hole through which the brass desired time, the pipe and its contents were quenched in oil. shear pin was inserted.

Length of heat treatment 0 hours hour 6% hours 24 hours Minutes Minutes Minutes Minutes to failure to failure to failure to failure Temperature of AS C AS- AS- C, AS C, treatment F.) S C S C min. S C min,

NOTE.S=suliurized: C =control.

EXAMPLE 2 Approximately 10 minutes was usually required for the pins 55 ln this set of runs the high-temperature treatment was car-' ried out in air.

Eighteen Falex pins and 36 Falex jaws (batch C) were employed. Three sets (one pin and two jaws per set) were subject fided set. Care was taken prior to and during the heat treat not to coating treatment in each of the oil compositions shown in to damage the sulfide coating which was most fragile. Heat table 111.

TABLE 111 Wt. percent Active chlorine and/or 011 Coating additive Additivev suliui A BasroilEx.l r r d Sulfurized sperm 01].. 0.8-1 1 (S) 0.18 Active sulfur 0. J (S) 0. it (.hlorinated parailins (40% active 2. 25 (Cl) 0.5!

chlorine). Active sulfur chlorinated parailins I 0. .1 (S) 0.!) (40% Cl/1V4 chlorine). l 2. 25 (Cl) 0. .1 i Sulfur chlorinated lard (33 wt. pvri (S) 3.66 (S) 1.22 cont). 1 (Cl) 3.16 (Cl) 1.05

jaws were then removed from the beakers and carefully cleaned with naphtha.

The high-temperature heat treatments in this example for all runs were made at l,200 F. for 6% hours in air. Prior to the high-temperature treatment, each set was wrapped in doublelayer stainless steel foil. After the air, heat treatment, the pin and jaws in most cases were covered by heavy scale that required vigorous cleaning to remove it. As much scale and stain as possible was removed with naphtha and paper towels. Then the pins and jaws were cleaned to the shiny metal surface with a copper tubing wire brush used with base oil followed with crocus cloth. The cleaned pins and jaws were then tested on the apparatus and in the manner described in exampie 1. Failure occurred in both the Falex pin and the brass shear pins in this set of runs as shown in table IV.

The invention claimed is:

the range of 900 to 2,000 F. 2. A process according to claim I wherein (a) comprises contacting the ferrous metal with a petroleum mineral oil containing active sulfur, chlorine or mixtures thereof.

3. The process according to claim 2 wherein said contacting is at a temperature in the range of 900 to 2,000 F.

4. The process according to claim 3 wherein an iron sulfide coating is formed.

5. The process according to claim 4 wherein the oil contains 0.5 and i5 percent sulfur.

6. The process according to claim 4 wherein the oil contains 0.5 to 15 percent chlorine.

7. The process according to claim 3 wherein the heating is carried on for 2 to 48 hours.

8. The process according to claim 1 wherein (b) is carried on for a period of time of 9% to 24 hours.

TABLE IV.-TEST RESULTS (HIGH TEMPERATURE TREATMENT OF FALEX PINS AND JAWS) Time to failure Type of Coating composition Minutes Seconds failure Run 1 2 Shear pin. Run 2 Base oil 6 54 Do. Run 3 0 9 Do.

A 1. 33 Run 4.. 3 46 Shear pin. Run 5.. Base oil plus sulferized sperm oil 0 29 D0. Run 6 0 41 Do.

Average, min 1. 7

Run 7 2 58 Shear pin. Base oil plus 0.9 wt. percent active sulfur 2 47 Falex pin.

l 17 Do. Average, min 2. 4

D I 14 19 Falex pin.

18 3 11 55 Shear pin. 15. 1

, 4 37 Falex pin. Base oil plus 0.0 wt. percent active sulfur, 2.25 wt. percent chlorinated paraffins 2 8 21 Do.

8 42 3 Average, min 7. 6

Run 16 10 33 Falex pin. Run 17. Sulfur chlorinated lard 9 46 D0- Run 18 10 23 Do.

Average, min 10. 2

l Badly stainednot cleaned to shiny metal-mot employed in average time to failure. 

2. A process according to claim 1 wherein (a) comprises contacting the ferrous metal with a petroleum mineral oil containing active sulfur, chlorine or mixtures thereof.
 3. The process according to clAim 2 wherein said contacting is at a temperature in the range of 900* to 2,000* F.
 4. The process according to claim 3 wherein an iron sulfide coating is formed.
 5. The process according to claim 4 wherein the oil contains 0.5 and 15 percent sulfur.
 6. The process according to claim 4 wherein the oil contains 0.5 to 15 percent chlorine.
 7. The process according to claim 3 wherein the heating is carried on for 2 to 48 hours.
 8. The process according to claim 1 wherein (b) is carried on for a period of time of 1/2 to 24 hours. 